1. Field
The present invention relates to a semiconductor memory device and a method of manufacturing the same, and more particularly, to a nonvolatile memory device and a method of manufacturing the same.
2. Discussion of Related Art
In order to improve a degree of integration of a semiconductor memory device, a 3D semiconductor memory device in which a memory cell arrangement is implemented to have three dimensions has been suggested. Especially, various technologies for implementing a memory cell arrangement of a NAND flash memory device that is a nonvolatile memory device to have three dimensions have been suggested.
The NAND flash memory device includes a plurality of memory strings. Each memory string includes a plurality of memory cells connected in series between a first select transistor and a second select transistor. In order to implement the memory string in a 3D structure, the first select transistor, memory cells, and the second select transistor are formed along a channel layer protruding from an upper portion of the substrate.
The channel layer of the 3D nonvolatile memory device is formed by depositing a polysilicon layer along surfaces of channel holes passing through insulation layers and conductive layers alternately stacked on the substrate. The polysilicon layer has larger resistance than that of single crystalline silicon. Accordingly, channel current flowing along the channel layer formed of the polysilicon layer when the nonvolatile memory device is operated is low, so that reliability of the nonvolatile memory device may deteriorate.
In order to improve channel current, the channel layer may be formed by filling inside the channel hole with a polysilicon layer. In this case, leakage current is increased, so that reliability of the nonvolatile memory device may deteriorate.